Mirroring your dog during play can help you connect and co-regulate. Play-fighting is a great way to regulate the nervous system and start to feel safety within activated states.
Your dog should have a soft mouth when you play! Raise the intensity slowly to be sure you don't trigger a traumatized dog.
You want the dog (and yourself) to stay within the window of tolerance.
Play serves as a co-regulating tool because the process of interacting with others during play creates a shared emotional experience that influences both individuals' nervous systems, helping them to regulate emotions, manage stress, and develop self-regulation skills.
Dogs will only play when they feel safe. So it becomes an important sign for you, because when your dog is able to play they are feeling good! And when they are unable to engage in play, it could be a sign that you need to adjust the environment or work on creating more safety for your dog's nervous system to down-regulate.